Europhys. Lett.
Volume 68, Number 3, November 2004
Page(s) 426 - 432
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 06 October 2004
Europhys. Lett., 68 (3), pp. 426-432 (2004)
DOI: 10.1209/epl/i2004-10208-4

Extremely large nonlinear absorption cross-sections in organic polymeric chains

Swapan K. Pati

Theoretical Sciences Unit, Jawharlal Nehru Center for Advanced Scientific Research Jakkur Campus - Bangalore 560 064, India

received 17 May 2004; accepted in final form 2 September 2004
published online 6 October 2004

We have considered one-dimensional organic conjugated polymeric systems to study the two-photon absorption (TPA) processes. The symmetrized density matrix renormalization group (SDMRG) method has been used to compute the low-energy photonic states and the TPA coefficients, for an extended Hubbard model. We find that the TPA coefficients diverge when the ground state of the system changes from the spin-density wave (SDW) state to the charge-density wave (CDW) state. Although in both phases the system is an insulator, the one-photon and two-photon gaps almost become equal near the transition point. The reason for the TPA coefficients to diverge is the near-degeneracy of these photonic states with strong electric dipole couplings at the transition point region. The picosecond scale nonlinear absorption processes observed in charge transfer insulating systems can be explained due to the formation of a triplet band below the lowest optically allowed state, based on our model calculations.

71.10.Fd - Lattice fermion models (Hubbard model, etc.).
71.35.-y - Excitons and related phenomena.
78.67.-n - Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures.

© EDP Sciences 2004